<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <script type="text/javascript">
        //undefined是继承nill出现的，所有两个值是相等
        var var_01=undefined;
        var var_02=null;
        if (var_01==var_02){
            console.log('两个变量的值相等')
        }else{
            console.log('两个变量的值不等')
        }
        if (var_01===var_02){
            console.log('两个变量的值相等')
        }else{
            console.log('两个变量的值不等')
        }
    </script>
</head>
<body>

</body>
</html>